For cold-blooded animals, the colder it gets—the harder life gets. As temperatures fall, lizards sprint slower, fish swim slower, and frogs jump shorter distances. Life-sustaining skills such as outrunning predators and foraging for food become insurmountable challenges. So it's not surprising that most cold-blooded animals, also known as ectotherms, remain inactive during the cooler parts of the day or avoid frosty habitats altogether. Most cold-blooded animals that is, except for chameleons.
It turns out that chameleons aren't your average ectotherm. Some chameleons live in alpine habitats above 3,500 m where temperatures can sometimes dip below freezing. Despite the cold, the chameleons can forage for food efficiently at low temperatures—temperatures at which other ectotherms grind to a halt. Just how chameleons keep on feeding at temperatures when their muscles should seize-up has been a mystery—until now.
New research by Christopher Anderson and Stephen Deban of the University of South Florida has revealed that chameleons can keep eating at chilly temperatures thanks to their ballistic tongues. The unique design of their tongues means that at temperatures when other muscles in the body are too cold to function, the tongue can still do its job.
Chameleons are cryptic, sit-and-wait predators. This means that they don't stalk or chase their quarry. Instead they sit motionless, blending into their surroundings, waiting for locusts, grasshoppers, crickets, or other insects to stumble within reach. Then, in a single burst, the chameleon launches its long sticky tongue in the direction of its prey. The tongue accelerates at an astonishing 41g and, if the chameleon has aimed well, the prey stands little chance of escape.
The key to how chameleon tongues keep working at cool temperatures lies in the fact that they are not powered by conventional muscles. Instead, the tongue of a chameleon is propelled by what is known as an elastic-recoil mechanism. Collagen tissue within the tongue is slowly stretched by a muscle called the tongue accelerator muscle. This stretching action stores up energy within the coiled tongue in the same way the stretched string of a bow stores energy to launch an arrow. When the coiled tongue of a chameleon is released, the tongue launches from the mouth with impressive speed without the need for muscular work. After release, the accelerator muscle slowly recoils the tongue.
Christopher Anderson and Stephen Deban used high-speed cameras to film chameleons as they feed on crickets at different temperatures. They measured the speed at which the chameleons ejected their tongues from their mouth and found that although there was some decrease in tongue speed at lower temperatures, feeding performance remained high.
Since chameleons can feed at low temperatures, they can occupy niches that are too cold and therefore unavailable to other lizards.
Anderson, C., & Deban, S. (2010). Ballistic tongue projection in chameleons maintains high performance at low temperature Proceedings of the National Academy of Sciences, 107 (12), 5495-5499 DOI: 10.1073/pnas.0910778107
Photo © CathyKeifer / iStockphoto.
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